Delegates at the TSSA's annual conference agreed to campaign in favour of a second referendum, and said Britain should remain in the EU if voters reject the deal Theresa May comes back with.

The union also committed itself to campaigning to ensure that voters aged 16 and 17 are able to vote in any second referendum.

"Our members have voted overwhelmingly for the voice of our members across the transport and travel industries to be injected into the national debate on Brexit," Mr Cortes said.

"It’s now very clear TSSA members don’t trust the Tories to deliver a Brexit deal that works for ordinary people.

"And now the worrying consequences of Brexit in Tory hands are becoming clearer by the day, they want their voice heard through a referendum which will act as a much needed safety valve to the process."

Mr Cortes - who backed Mr Corbyn in the 2016 Labour leadership election - has previously urged the party to "defend our people against the boss class" by seeking to halt exit from the EU.

Eloise Todd of the pro-Remain Best for Britain pressure group welcomed the union's support for a fresh say on Brexit.

"It's fantastic that the TSSA union has joined calls for a people's vote on the terms of Brexit between the Government's deal and the EU membership deal we currently have," she told PoliticsHome.

The campaign chief added: "An important part of democracy is informed choice - and now the government's deal is finally starting to take shape people across the country will be able to see which deal leaves them better off.

"That's why we called last Friday for Brexit to be resolved one way or another by the end of next March - is it the government deal or our EU terms? It's simple: may the best deal win. It's time to give the final say to the citizens of the UK."

The TSSA's move follows a drive from some of Mr Corbyn's own backbenchers for a fresh vote, with London MPs including Chuka Umunna, Margaret Hodge, Wes Streeting, Stella Creasy and Tulip Siddiq putting their names to a letter calling for a new referendum earlier this month.

Welsh MPs Anna McMorrin and Tonia Antoniazzi, who both serve as aides to Mr Corbyn’s Shadow Cabinet, meanwhile gave their backing to a cross-party campaign for a ‘people’s vote’ on the final Brexit deal, a move that saw them reprimanded by party chiefs.

Owen Smith, the former shadow Northern Ireland secretary, was sacked from the Labour frontbench in March after openly calling for a second referendum to "ask if Brexit remains the right choice for the country".

But, speaking earlier this year, Mr Corbyn appeared to firmly rule out backing a fresh vote, saying his party was "not asking for a second referendum".

"The referendum gave us the result, it did. We wanted to remain and reform but that ship has sailed," he told the BBC.